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  • 1.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Z
    Royal Institute of Technology, Department of Aeronautical and Vehicle Engineering, Stockholm.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Influence of defects on fatigue crack propagation in laser hybrid welded eccentric fillet joint2011In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 78, no 10, p. 2246-2258Article in journal (Refereed)
    Abstract [en]

    Fatigue cracking of laser hybrid welded eccentric fillet joints has been studied for stainless steel. Two-dimensional linear elastic fracture mechanics analysis was carried out for this joint geometry for four point bending load. The numerical simulations explain for the experimental observations why the crack propagates from the lower weld toe and why the crack gradually bends towards the root. Lack of fusion turned out to be uncritical for the initiation of cracks due to its compressive stress conditions. The linear elastic fracture mechanics analysis has demonstrated in good qualitative agreement with fatigue test results that lack of fusion slightly (<10%) reduces the fatigue life by accelerating the crack propagation. For the geometrical conditions studied here improved understanding of the crack propagation was obtained and in turn illustrated. The elaborated design curves turned out to be above the standard recommendations

  • 2.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Z.
    Royal Institute of Technology.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander
    Häggblad, Hans-Åke
    The influence of surface geometry and topography on the fatigue cracking behaviour of laser hybrid welded eccentric fillet joints2010In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 265, no 6, p. 1936-1945Article in journal (Refereed)
    Abstract [en]

    Laser hybrid welding of an eccentric fillet joint causes a complex geometry for fatigue load by four point bending. The weld surface geometry and topography were measured and studied in order to understand the crack initiation mechanisms. The crack initiation location and the crack propagation path were studied and compared to Finite Element stress analysis, taking into account the surface macro- and micro-geometry. It can be explained why the root and the upper weld toe are uncritical for cracking. The cracks that initiate from the weld bead show higher fatigue strength than the samples failing at the lower weld toe, as can be explained by a critical radius for the toe below which surface ripples instead determine the main stress raiser location for cracking. The location of maximum surface stress is related to a combination of throat depth, toe radius and sharp surface ripples along which the cracks preferably propagate.

  • 3.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Zuheir
    Kungliga tekniska högskolan, KTH.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Kaplan, Alexander
    Fatigue behaviour study of laser hybrid welded eccentric fillet joints: Part I2009In: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th - 26th August 2009 in Copenhagen / [ed] Erling Dam Mortensen, Kgs. Lyngby: ATV-SEMAPP , 2009Conference paper (Refereed)
    Abstract [en]

    Welded joints are a major component that is often responsible for causing a structure failure or for being the point at which fatigue cracking initiates and propagates. Despite tremendous research efforts, the understanding of fatigue behaviour is still limited, particularly for new techniques like laser hybrid welding. Beside a comprehensive state-of-the-art study, the paper presents a fatigue study of laser hybrid welded eccentric fillet joint of stainless steel of 10 mm thickness, with 5 mm displacement. Motivation is to study the influence of the surface geometry shape on fatigue performance under a four point bending test. 13 samples were produced, measuring the toe radii and testing under constant amplitude loading with stress ratio R=0. Different techniques have been used to measure local weld geometry, like plastic replica, a 3D optical profiler and a 3D-digitizer. The influence of the local weld geometry, like the toe radii, on the stress concentration was studied by FE-analysis. Occasionally lack of fusion was observed, which was taken into account in the FE-analysis. Based on the nominal stress approach, SN-curves were designed for laser hybrid welded eccentric fillet joints. Macro hardness tests were carried out and the crack surfaces were observed in order to detect crack initiation and propagation. Correlations between the toe radii, the corresponding stress maxima and crack initiation locations were studied between the different samples and even along the welds.

  • 4.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Zuheir
    Kungliga tekniska högskolan, KTH.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Fatigue behaviour study of laser hybrid welded eccentric fillet joints: Part II: State-of-the-art of fracture mechanics and fatigue analysis of welded joints2009In: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th - 26th August 2009 in Copenhagen / [ed] Erling Dam Mortensen, Kgs. Lyngby: ATV-SEMAPP , 2009Conference paper (Refereed)
    Abstract [en]

    Simplified fatigue and fracture mechanics based assessment methods are widely used by the industry to determine the structural integrity significance of postulated cracks, manufacturing flaws, service-induced cracking or suspected degradation of engineering components under normal and abnormal service loads. In many cases, welded joints are the regions most likely to contain original fabrication defects or cracks initiating and growing during service operation. The welded joints are a major component that is often blamed for causing a structure failure or for being the point at which fatigue or fracture problems initiate and propagate. Various mathematical models/techniques for various classes of welded joints are developed by analytically or by simulation software's that can be used in fatigue and fracture assessments. This literature survey compiled useful information on fracture and fatigue analysis of various welded joints. The present review is divided into two major sections- fracture mechanics and fatigue analysis with widely used models. A survey table is also introduced to get the outlook of research trend on fatigue and fracture over last 3 decades. Although tremendous research effort has been implemented on fatigue and fracture analysis of conventional welding, research on relatively new welding technology (laser welding, hybrid laser welding) is still limited and unsatisfactory. In order to give guarantee or make welding standard for new welding technology, further research is required in the field of fatigue and fracture mechanics including FEM and multi-scale modeling.

  • 5.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Zuheir
    Royal Institute of Technology.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Kaplan, Alexander
    Geometrical aspects of the fatigue behaviour of laser hybrid fillet welds2009In: Proceedings of the Fatigue Design Conference, Cetim , 2009Conference paper (Refereed)
  • 6.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Zuheir
    Royal Institute of Technology.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander
    Häggblad, Hans-Åke
    The effects of surface topography and lack of fusion on the fatigue strength of laser hybrid welds2009In: Congress proceedings: ICALEO, 28th International Congress on Applications of Lasers & Electro-Optics : November 2 - 5, 2009 - Orlando, FL : Laser Materials Processing Conference, Laser Microprocessing Conference, Nanomanufacturing Conference, poster presentation, gallery, Orlando, Fla: Laser institute of America , 2009, p. 38-46Conference paper (Refereed)
    Abstract [en]

    The geometrical aspects of laser hybrid welding before, during and after the process differ from autonomous laser welding and from arc welding. When studying the fatigue behaviour of laser hybrid welded fillet joints we identified that the microgeometry, i.e. the surface ripples can be more critical than the macrogeometry of the weld surface and even than lack of fusion (LOF), which frequently was detected. The plastic replica method was applied to measure the toe radii at the weld edges while the topography was identified by interferometric profilometry. From metallurgical analysis of the joint interface the tendency to LOF can be explained. Stress analysis was carried out by FEA for the complex joint geometry and bending load situation, showing maximum stress on the weld toes, even when including LOF. It was shown that the position and value of the maximum stress depends on a non-trivial combination of the weld geometry, including possible LOF, and the surface topography. Thus it can be explained that at compressive stress conditions LOF does not contribute significantly to the fatigue strength of laser hybrid welds while the surface topography does. Recommendations for defining and in turn avoiding critical geometrical aspects during the welding process are discussed.

  • 7.
    Berg, Sven
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    High-pressure compaction modelling of calcite (CaCO3) powder compact2011In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 206, no 3, p. 259-268Article in journal (Refereed)
    Abstract [en]

    Numerical simulation of manufacturing processes with working conditions at high pressure (above 1 GPa) requires constitutive data of the powder for the whole range of pressure and density. Most of the test apparatuses commonly used to obtain such data is only working in the lower pressure regions. Because of the absence of high-pressure data, many parameters have to be guessed or extrapolated. A material used in high-pressure applications is Calcite (CaCO3). The material can be used as an insulator in high-pressure capsules it is also a common material in the earth core. An apparatus often used to generate high pressure during compaction is the Bridgman anvil apparatus. In this work experimental tests with a Bridgman anvil set-up using Calcite powder discs with different thicknesses were done. A nonlinear elastic-plastic cap model was developed to model the behaviour of powder material from low pressure and loose state to high pressure and solid state. The constitutive model was implemented in a finite element code. The constitutive data were identified by optimization of experimental data. Validation was done by numerically reproduce the mechanical behaviour of uni-axially pressing Calcite to different pressure (up to 5 GPa) including unloading. The load-displacement curves, density distribution and the surface displacement were measured and compared to the finite element results. The results of the compaction simulations agree reasonably well with the experimental results.

  • 8. Berg, Sven
    et al.
    Jonsén, Pär
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Experimental characterisation of CaCO3 powder mix for high-pressure compaction modelling2010In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 203, no 2, p. 198-205Article in journal (Refereed)
    Abstract [en]

    The mechanical properties of powders at high pressures are difficult to measure and therefore such data are rarely reported in open literature. Available test equipment mainly operates in the low-pressure region, 0-200 MPa. Calcite (CaCO3) is a mineral suitable for high-pressure processes, e.g. sintering of diamond compacts. It is also a very common material in the earth core and therefore of interest for geoscientists. In order to model the processes in the high-pressure region (above 1 GPa), knowledge of the mechanical properties of the powder in the entire pressure range is needed. Experimental studies have been conducted to investigate the pressure-density relationship of a CaCO3 powder and also to correlate the relative density to elastic and strength properties using experimental results. Further, a methodology has been introduced to provide a foundation for an elastic-plastic constitutive model. The mechanical behaviour of a CaCO3 powder mix has been investigated using the Brazilian disc test, uniaxial compression testing and closed die experiments. The experiments showed increasing elastic modulus and strength with increasing density. An empirical expression of the dependence of the bulk modulus on density has also been introduced.

  • 9.
    Berg, Sven
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Experimental characterization of CaCO3powder for use in compressible gaskets up to ultra-high pressure2012In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 215-216, p. 124-131Article in journal (Refereed)
    Abstract [en]

    The purpose of this study was to investigate the compaction properties for a CaCO3 powder mix up to ultra-high pressure (10GPa) and how these properties affect the gasket behaviour. Different parameters of the powder are investigated, i.e. initial density and internal moisture. A set-up, supporting the outer diameter of the compact, commonly used for gaskets in the belt apparatus was also investigated. The experimental results are in terms of pressure instrumentation in the Bridgman anvil apparatus together with load–displacement curves of the powder compacts. The instrumentation is done so that it can be used to calibrate constitutive models.

  • 10.
    Berg, Sven
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Carlson, Johan E.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    High pressure characterization and modelling of CaCO3 powder mix in the Bridgman anvil apparatus2012In: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 32, no 4, p. 490-508Article in journal (Refereed)
    Abstract [en]

    For investigating high pressure sintering processes, numerical models can be used. This will demand material models which give realistic mechanical response throughout the whole parameter space of the actual process. As the pressures become higher, the material density approaches its full theoretical value and the elastic part of the material properties becomes increasingly important. In this investigation, Poisson's ratio was determined using ultrasonic pulse-echo measurements. A new elastic model and an improved plasticity model were implemented into a user-defined material subroutine in a finite element (FE) code. To experimentally investigate the load displacement response and pressure distribution in powder compacts during pressing, a pressure instrumented Bridgman anvil apparatus was used. Validation of the FE model was conducted against experimental data from pressing experiments using two different start densities. The results show that the simulation model is indeed capable of reproducing load–thickness curves and pressure profiles reasonable close to the experimental curves.

  • 11.
    Berg, Sven
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Frictional behaviour of CaCO3 powder compacts2012In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 228, p. 429-434Article in journal (Refereed)
    Abstract [en]

    During powder compaction processes friction has an influence on the final shape and properties of components. It is therefore important to understand how the friction influences the compaction process. Since detailed friction measurements of the powder compact-tool interface are rare, simulation models of the powder compaction process often involve a more accurate description of the frictional behaviour. This limits the accuracy of the simulated results. More accurate numerical models can give improved results, especially in regards to the evolution of density and its distribution within the powder compacts.This study is as a step towards more advanced friction models for powder compaction simulations. A universal tribometer has been used to investigate the frictional behaviour of contact interfaces between a carbide counter surface and CaCO3 powder compacts with different densities. Both static and dynamic frictional properties were measured in a variety of conditions to build a fundamental foundation for friction modelling in powder compaction simulations.The results show that increasing the powder compact density decreases the dynamic friction coefficient but that the static friction coefficient remains fairly constant. The measured friction coefficient can be used to improve the simulation of a powder compact process. Also investigated is the change in friction coefficient that occurs in the compaction process when the surfaces are worn such that loose powder appears in the interface between the tool and the powder compact. This behaviour is important to take into account to accurately describe the compaction process.

  • 12.
    Cante, J.
    et al.
    E.T.S. d’Enginyeries Industrial i Aeronáutica de Terrassa, Technical University of Catalonia (UPC), Campus Terrassa UPC.
    Dávalos, C.
    International Center for Numerical Methods in Engineering (CIMNE), C/. Gran Capitan s/n, 08034 , Barcelona.
    Hernández, J.A.
    E.T.S. d’Enginyeries Industrial i Aeronáutica de Terrassa, Technical University of Catalonia (UPC), Campus Terrassa UPC.
    Oliver, J.
    E.T.S. d’Enginyers de Camins, Canals i Ports de Barcelona, Technical University of Catalonia (UPC), Campus Nord UPC.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Gustafsson, Gustaf
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    PFEM-based modeling of industrial granular flows2014In: Computational Particle Mechanics, ISSN 2196-4378, Vol. 1, no 1, p. 47-70Article in journal (Refereed)
    Abstract [en]

    The potential of numerical methods for the solution and optimization of industrial granular flows problems is widely accepted by the industries of this field, the challenge being to promote effectively their industrial practice. In this paper, we attempt to make an exploratory step in this regard by using a numerical model based on continuous mechanics and on the so-called Particle Finite Element Method (PFEM). This goal is achieved by focusing two specific industrial applications in mining industry and pellet manufacturing: silo discharge and calculation of power draw in tumbling mills. Both examples are representative of variations on the granular material mechanical response—varying from a stagnant configuration to a flow condition. The silo discharge is validated using the experimental data, collected on a full-scale flat bottomed cylindrical silo. The simulation is conducted with the aim of characterizing and understanding the correlation between flow patterns and pressures for concentric discharges. In the second example, the potential of PFEM as a numerical tool to track the positions of the particles inside the drum is analyzed. Pressures and wall pressures distribution are also studied. The power draw is also computed and validated against experiments in which the power is plotted in terms of the rotational speed of the drum.

  • 13. Coccoz, G.
    et al.
    Bellet, M.
    Lécot, R.
    Ackermann, L.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Cold compaction of iron powder: experiments and simultation.1994In: PM '94 : Congrès Mondial de Métallurgie des Poudres - Powder Metallurgy World Congress, Paris, 6 - 9 juin 1994: Société Française de Métallurgie et de Matériaux; European Powder Metallurgy Association, Les Ulis: Ed. de Physique , 1994Conference paper (Refereed)
  • 14.
    Cocks, Alan C F
    et al.
    University of Oxford.
    Gethin, David T
    University of Swansea.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kraft, Torsten
    Fraunhofer IWM.
    Coube, Olivier
    Plansee SE.
    Compaction models2007In: Modelling of powder die compaction, London: Encyclopedia of Global Archaeology/Springer Verlag, 2007, p. 43-64Chapter in book (Other academic)
  • 15. Eriksson, Magnus
    et al.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Berggren, C.
    Nobel Biocare AB.
    Andersson, M.
    Nobel Biocare AB.
    Holmersson, R.
    Nobel Biocare AB.
    Carlström, E.
    Swedish Ceramic Institute, PO Box 5403, SE-402 29 Göteborg.
    New semi-isostatic high velocity compaction method to prepare titanium dental copings2004In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 47, no 4, p. 335-342Article in journal (Refereed)
    Abstract [en]

    A new method to prepare titanium dental copings from titanium powder was tested, involving high velocity compaction and various elastic forms, which were used to achieve a semi-isostatic effect during the impact. The tooth preparation die (mandrel) and the powder were placed inside an elastic form. The impact struck the elastic form, and the powder was compacted against the tooth preparation die. Several different elastomers were tested to find the best one. Cross-sections of the powder bodies were studied for density variations. The soft, flexible elastomer worked best to compact the powder. The highest densification could be focused closest to the mandrel where the coping should be milled out. The density in the highest density areas could locally reach 98-99%. If the method with elastic forms could be optimised to give as high a density as without elastic forms, a lower shrinkage and possible deformation of the copings could be reached.

  • 16. Federzoni, L.
    et al.
    Riedel, H.
    Coube, O.
    Oldenburg, Mats
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Gethin, D.
    State of the art review - Comparison of computer models representing powder compaction process.1999In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 42, no 4, p. 301-311Article in journal (Refereed)
  • 17. Frachon, A.
    et al.
    Imbault, D.
    Doremus, P.
    Federzoni, L.
    Brunet, R.
    Reyre, M.
    Wikman, Bengt
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Oldenburg, Mats
    Sensitivity of numerical simulation to input data2000In: Proceedings of PM2000 Powder metallurgy world congress and exhibition: November 12 - 16, 2000, Kyoto International Conference Hall, Japan / [ed] Koji Kosuge; Hiroshi Nagai, Tokyo: Japan Society of Powder and Powder Metallurgy , 2000Conference paper (Refereed)
  • 18. Gavelin, Anders
    et al.
    Lindquist, Mats
    Umeå university.
    Häggblad, Hans-Åke
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Methodology for mass minimisation of a seat structure with integrated safety belts constrained by biomechanical responses on the occupant in frontal crashes2010In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 15, no 4, p. 343-355Article in journal (Refereed)
    Abstract [en]

    A methodology using finite element (FE) modelling and simulation with a property-based model (PBM) is presented. A generic 3-D FE model of a seat structure with a three-point seat-integrated safety belt configuration was established. A 50th percentile Hybrid III FE dummy model was used as occupant. Metamodelling techniques were used in optimisation calculations performed in two steps. Step 1: Six separate optimisations minimising biomechanical responses of the FE dummy model. Step 2: Four separate optimisations with different start values of the design variables, with the total mass of the seat structure as objective function and with the minimised biomechanical responses from Step 1 as constraint values. Six design variables were used in both Step 1 and Step 2. The four optimisations performed in Step 2 generated four different results of the total mass. Thus, different local minima were found instead of one single global minimum. The presented methodology with a PBM may be used in a concept design phase. Some issues concerning the FE model suggest further improvement.

  • 19. Gustafsson, Gustaf
    et al.
    Cante, Juan Carlos
    Escola Tècnica Superior d'Enginyeries Industrial i Aeronàutica de Terrassa.
    Jonsén, Pär
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Weyler, Rafael
    Escola Tècnica Superior d'Enginyeries Industrial i Aeronàutica de Terrassa.
    Comparison of smoothed particle method and particle finite element method in applied granular flow problems2009In: Particle-Based Methods: Fundamentals and Applications / [ed] Eugenio Oñate; Roger Owen, Barcelona: International Center for Numerical Methods in Engineering (CIMNE), 2009, p. 204-207Conference paper (Refereed)
    Abstract [en]

    Traditionally, discrete element (DE) method and finite element (FE) method are used in numerical simulation of granular flow problems. A drawback with the (DE) method is the limitations in modelling the extreme large number of particles, which normally are in real granular flow problems. With a numerical method based on continuum mechanics modelling like the FE-method, the problems can be solved with less computation particles. However, the limitations of the FE-method have been pointed out to be when extremely large deformation needs to be captured. Granular flow problem motions produce large distortions of the mesh and ruin the convergence of the problem. The purpose of this paper is to compare two alternative continuum based methods, the Particle Finite Element Method (PFEM) and the Smoothed Particle (SP) method, to model two different granular flow problems.

  • 20. Gustafsson, Gustaf
    et al.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Simulation of metal powder die filling processes using smoothed particle hydrodynamics method2007In: Proceedings: PM in Toulouse - at the forefront of european technology; 15 - 17 October 2007, Pierre Baudis Congress Centre, Toulouse, France, Shrewsbury: European powder metallurgy association , 2007, Vol. 3 : Powder pressing : sintering ; full density & alternative consolidation ; modelling ; secondary & finishing operations, p. 311-316Conference paper (Refereed)
    Abstract [en]

    The die filling is an important stage in the manufacturing process of powder metallurgical components as proceeding stages are influenced by the powder distribution achieved by the filling process. Numerical simulation is a powerful tool in process development and can be used to increase the knowledge about the filling behaviour. In this work smoothed particle hydrodynamics (SPH) method is used to simulate shoe filling of metal powder into simple and stepped dies. An elastic-plastic material model is used as constitutive model where the material parameters are estimated using results from filling rate experiments and loose powder shear tests. The powder flow behaviour and packing density is simulated and compared with experimental results. The results indicate that SPH simulations can capture major observed features of powder die filling.

  • 21.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Simulation of the confined compression test of iron ore pellets using random distributed 3D multi particle finite elements2010Conference paper (Refereed)
    Abstract [en]

    In this work, a multi particle finite element model is used to simulate the axial compression of iron ore pellets inside a steel cylinder. Each individual pellet is discretized with a 3D finite element mesh. From experiment, the load, displacement and the circumferential strain are measured. Experimental results are compared with simulation results.

  • 22.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Characterization modelling and validation of a two-point loaded iron ore pellet2013In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 235, p. 126-135Article in journal (Refereed)
    Abstract [en]

    Iron ore pellets are sintered, centimetre-sized spheres of ore with high iron content. Together with carbonized coal, iron ore pellets are used in the production of steel. In the transportation from the pelletizing plants to the customers, the iron ore pellets are exposed to different stresses, resulting in degradation of strength and in some cases fragmentation. For future reliable numerical simulations of the handling and transportation of iron ore pellets, knowledge about their mechanical properties is needed. This paper describes the experimental and numerical work to investigate the mechanical properties of blast furnace iron ore pellets. To study the load deformation behaviour and the fracture of iron ore pellets, a number of point load tests are carried out and analysed. Material parameters for an elastic–plastic constitutive model with linear hardening for iron ore pellets are derived and expressed in terms of statistical means and standard deviations. Two finite element models are developed for different purposes. For the material parameter determination, a perfectly spherical model is used. The constitutive model is validated with a finite element model based on a representative optically scanned iron ore pellet. The proposed constitutive model is capturing the force displacement relation for iron ore pellets in a two-point load test. A stress based fracture criterion which takes the triaxiality into account is suggested and calculated as the maximum equivalent effective stress dependent on the three principal stresses at fracture. The results of this study show that the equivalent effective stress in the vicinity of the centre of an irregular model of an iron ore pellet is very close to the results of a model of a perfectly spherical iron ore pellet. The proposed fracture criterion indicates fracture in the representative iron ore pellet model coincident with the location of the crack developed during the test of the optically scanned iron ore pellet.

  • 23.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Modelling and simulation of iron ore pellets2013Conference paper (Refereed)
    Abstract [en]

    Transportation and storage are important parts in the process chain for producers of iron ore pellets. Knowledge and optimization of these processes are very important for further efficiency progress and increased product quality. The existence of a numerical simulation tool with accurate material characteristics will significantly increase the possibility to predict critical forces in developing new and existing transportation and storing systems and thereby decrease the amount of damaged, fractured or crushed pellets (fines). In this work modelling and simulation of iron ore pellets are carried out at different length scales. An elastic plastic granular continuum flow model for iron ore pellets using smoothed particle (SP) method is presented [1]. The model is used to model iron ore pellets silo flow. A finite element (FE) model of single iron ore pellets is also worked out with statistical data for an elastic plastic constitutive model with a fracture criterion [2]. The model is used to simulate loading and fracture on single iron ore pellets and is validated with a two point load test. In order to find the relation between the behaviour of iron ore pellets at different length scales, e.g. compare the stresses in a silo to the critical stress inside a single iron ore pellet, modelling of iron ore pellets on an intermediate length scale is established. A multi particle finite element model (MPFEM) consisting of individual discretized models of the iron ore pellets is here presented [3]. An instrumented confined compression tests is developed for measuring the global response on a limited amount of iron ore pellets [4]. The experiment is used to validate the MPFEM model in terms of the amount of broken pellets.

  • 24.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Multi-particle finite element modelling of the compression of iron ore pellets with statistically distributed geometric and material data2013In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 239, p. 231-238Article in journal (Refereed)
    Abstract [en]

    The multi-particle finite element method (MPFEM) is used to simulate confined compression of iron ore pellets. The confined compression test consists of a cylindrical steel tube and two compressive platens. The iron ore pellets are confined by the tools and compressed. In the MPFEM model of the test, the iron ore pellets are represented by 1680 finite element (FE) discretised particles (7-16 mm). The size, shape and material properties of the pellets are statistically distributed. The contacts are modelled using the penalty stiffness method and Coulomb friction. The compression is simulated in two steps. In the first step, the iron ore pellet models are sparsely placed in the computational model of the steel tube and a gravity-driven simulation is conducted to make the pellets arrange themselves randomly. In a second step, the compression is simulated by a prescribed motion of the upper compressive platen. From the MPFEM simulation, the stresses inside the individual pellet models are evaluated, and the fracture probability of the iron ore pellets is derived and compared with experimental data. In addition, data on the global axial and radial stresses and axial displacement are presented and compared with experimental confined compression test data. The MPFEM model can reproduce the fracture ratio of iron ore pellets in uniaxial confined compression and is a feasible method for virtual fracture experiments of iron ore pellets.

  • 25.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Simulation of stresses in iron ore pellets for confined compression-tests using the multi particle finite element method2011Conference paper (Refereed)
    Abstract [en]

    Numerical simulation of the compaction of granular materials is an area of active research. One approach is to use deformable discrete elements of the individual particles using a 2D finite element (FE) mesh, see e.g. [1] and [2]. In this work, the axial compression of iron ore pellets inside a steel cylinder is studied and the individual particles are discretized with a coarse FE mesh in 3D. One possibility of this model is to study the stresses and strains inside the granular particles. Experiment and simulation of iron ore pellets in a confined compression test are done. The experiment consists of an upper and lower piston of thick circular steel plates surrounded by a 2 mm steel cylinder containing the iron ore pellets. The total mass of the iron ore pellets is 46.0kg. During a test, an axial load is applied on the lower piston to a certain level and then unloaded. Measured data are the force and displacement of the lower piston. In addition, strain gauges are measuring the circumferential strain in the middle of the steel membrane. Experimental compression tests between two plates of 18 randomly chosen iron ore pellets were done in order to characterize the load displacement behaviour of the individual pellets. FE models of the experimental tested pellets were carried out and simulated. Each pellet was discretized with an eight-node FE mesh. An elasto-plastic material model with linear hardening is used. The Young’s modulus, the plastic hardening modulus, and the yield stress of the material model were found by inverse modelling. Different material parameters were tested systematically in the FE model and compared with the experimental results until the same load displacement curve was obtained. A multi particle finite element model (MPFEM) was used to simulate the confined compression test. The iron ore pellets are represented in a quarter-model of the real experimental setup by 4756 discretized particles (7-16 mm) with a normal distribution measured from size distribution in the experiment. The contacts are modelled with the penalty stiffness method. The pistons are considered rigid in the simulation and the steel cylinder is modelled with thin elastic shell elements. The compression is simulated in two steps. In the first step, the iron ore pellets models are randomly sparse placed the cylinder and a gravity driven simulation is carried out where the pellets are arranged in the cylinder. In the second step, the compression is simulated by a prescribed displacement of the upper piston. Compared data from the experiment and simulation are; fill density, force-displacement curve and circumferential strain. A relation between the global stress state from the loading of the piston and the maximum stresses inside the individual iron ore pellets was carried out from the simulation. References [1] A.T. Procopio, A. Zavaliangos. “Simulation of multi-axial compaction of granular media from loose to high relative densities”, Journal of the Mechanics and Physics of Solids, 53 pp. 1523-1551, 2005. [2] D.T. Gethin, R.S. Ransing, R.W. Lewis, M. Dutko, A.J.L. Crook, “Numerical comparison of a deformable discrete element model and an equivalent continuum analysis for the compaction of ductile porous material”, Computers and Structures, 79 pp. 1287-1294, 2001.

  • 26.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Simulation of stresses in iron ore pellets for confined compression-tests using the multi particle finite element method2011Conference paper (Refereed)
  • 27.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Determination of bulk properties and fracture data for iron ore pellets using instrumented confined compression experiments2013In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 241, p. 19-27Article in journal (Refereed)
    Abstract [en]

    In this work, an experimental method for measuring the bulk properties and fracture loading relations for iron ore pellets is presented. Knowledge on the bulk behaviour and fracture data for iron ore pellets is of great importance for improving the material transportation systems and to increase the product quality. Trustworthy numerical simulations of iron ore pellets also demand reliable materials data for the models. Here, instrumented confined compression tests are carried out at different load levels. Measurement data of the axial and radial stresses and the axial displacement are recorded for each test. Measurements of fractured iron ore pellets are carried out at different loads giving rise to crushing up to 20% of the total material. From the measured data, the Poisson´s ratio, the bulk modulus and a plastic strain hardening function are determined. In addition, friction measurements of iron ore pellets are carried out at different loads and configurations. In conclusion, the test method developed here is usable for the determination of the bulk properties and fracture characteristics of iron ore pellets.

  • 28.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Nishida, Masahiro
    Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Japan, Nagoya Institute of Technology.
    High-rate behaviour of iron ore pellet2015In: EPJ Web of Conferences, ISSN 2101-6275, E-ISSN 2100-014X, Vol. 94, article id 5003Article in journal (Refereed)
    Abstract [en]

    Iron ore pellets are sintered, centimetre-sized spheres of ore with high iron content. Together with carbonized coal, iron ore pellets are used in the production of steel. In the transportation from the pelletizing plants to the customers, the iron ore pellets are exposed to different loading situations, resulting in degradation of strength and in some cases fragmentation. For future reliable numerical simulations of the handling and transportation of iron ore pellets, knowledge about their mechanical properties is needed. This paper describes the experimental work to investigate the dynamic mechanical properties of blast furnace iron ore pellets. To study the dynamic fracture of iron ore pellets a number of split Hopkinson pressure bar tests are carried out and analysed

  • 29.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Knutsson, Sven
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Experimental characterization of constitutive data of iron ore pellets2009In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 194, no 1-2, p. 67-74Article in journal (Refereed)
    Abstract [en]

    For trustworthy numerical simulations of iron ore pellets flow, knowledge about the mechanical properties of pellets is needed. In this work, an elastic-plastic continuum material model for blast furnace iron ore pellets is worked out from an experimental data. The equipment used is a Norwegian simple shear apparatus, designed for compression and shear test of granular material with a grain size less than 100 mm. It consists of a cylindrical cell filled with pellets surrounded by a rubber membrane and a rigid top and bottom. Two types of tests are performed. One test is pure compression and unloading and the second is shearing at different stress levels. Evaluation of these tests is performed and the elastic-plastic behaviour of iron ore pellets is characterized. Determined constitutive data are two elastic parameters and a yield function. The presented material model captures the major characteristics of the pellets even though it is too simple to completely capture the complex behaviour shown in the experiments.

  • 30.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Larsson, Simon
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Numerical Prediction of Fracture in Iron Ore Pellets During Handling and Transportation2017In: / [ed] Barry Wills, 2017Conference paper (Refereed)
    Abstract [en]

    Iron ore pellets are sintered, centimetre-sized spheres of ore with high iron content. Together with carbonized coal, iron ore pellets are used in the production of steel. During transportation and handling of iron ore pellets they are exposed to different loads, resulting in degradation of the strength and in some cases fragmentation. The aim of this work is to increase the knowledge of how to design the handling systems for iron ore pellets to decrease the amount of fractured materials in the flows. A numerical finite element model for iron ore pellets fracture probability analysis is presented with a stress based fracture criterion. The model is used to simulate different flows of iron ore pellets hitting guide plates and to predict the proportion of fractured iron ore pellets in the flow. The amount of fractured iron ore pellets are predicted at different flow velocities, showing good agreement with experimental measurements.

  • 31.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Nishida, Msahiro
    Nagoya Institute of Technology, Gokisocho, Showa-ku, Aichi.
    Larsson, Simon
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Fracture probability modelling of impact-loaded iron ore pellets2017In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 102, p. 180-186Article in journal (Refereed)
    Abstract [en]

    Blast furnace iron ore pellets are sintered, centimetre-sized ore spheres with a high iron content. Together with carbonized coal, iron ore pellets are used in the production of steel. In transporting pellets from pelletizing plants to customers, iron ore pellets are exposed to different static and dynamic loading situations, resulting in strength degradation and, in some cases, fragmentation. This can lead to a reduced gas flow in the blast furnace, which causes reduced quality in steel production. Reliable numerical simulations that can predict the ability of the pellets to endure their handling are important tools for optimizing the design of equipment for iron ore handling. This paper describes the experimental and numerical work performed to investigate the impact fracture behaviour of iron ore pellets at different strain rates. A number of split Hopkinson pressure bar tests with different striker velocities are carried out and analysed to investigate the strain rate dependency of the fracture strength of iron ore pellets. Fracture data for iron ore pellets are derived and expressed in terms of statistical means and standard deviations. A stress based, strain-rate dependent fracture model that takes triaxiality into account is suggested. The fracture model is used and validated with impact tests of iron ore pellets. In the validation experiment, iron ore pellets are fired against a steel plate, and the percentage of fractured pellets at different impact velocities are measured. Finite element simulations of the experiment are carried out and the probability of pellets fracturing during impact are calculated and compared with the experimental results. The agreement between the experiments and numerical simulations shows the validity of the model.

  • 32. Gustafsson, Gustaf
    et al.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Oldenburg, Mats
    Smoothed particle hydrodynamic simulation of iron ore pellets flow2007In: Materials Processing and Design: Modeling, Simulation and Applications: NUMIFORM 2007, Proceedings of the 9th International Conference on Numerical Methods in Industrial Forming Processes / [ed] José M. A. César de Sá; Abel D. Santos, Melville, NY: American Institute of Physics (AIP), 2007, p. 1483-1488Conference paper (Refereed)
    Abstract [en]

    In this work the Smoothed Particle Hydrodynamics (SPH) method is used to simulate iron ore pellets flow. A continuum material model describing the yield strength, elastic and plastic parameters for pellets as a granular material is used in the simulations. The most time consuming part in the SPH method is the contact search of neighboring nodes at each time step. In this study, a position code algorithm for the contact search is presented. The cost of contact searching for this algorithm is of the order of Nlog2N, where N is the number of nodes in the system. The SPH-model is used for simulation of iron ore pellets silo flow. A two dimensional axisymmetric model of the silo is used in the simulations. The simulation results are compared with data from an experimental cylindrical silo, where pellets are discharged from a concentric outlet. Primary the flow pattern is compared.

  • 33.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Smoothed particle simulation and validation of powder filling2015Conference paper (Refereed)
    Abstract [en]

    Powder pressing is often a complicated process as the behaviour of the powder material changes with increasing density. Manufactures tend to produce components with more complicated shapes which demand complex pressing equipment and methods. Mechanical properties of powder materials changes dramatically from the beginning to the end of the compaction phase. Previous investigations have shown that powder transfer and high powder flow during filling affects the strength of the final component significantly. Experimental studies combined with simulations is likely to improve the understanding of the filling stage, e.g. to explain the non-homogeneity of the density of powder pressed parts. This work covers both experimental measurements and umerical modelling of powder filling. Experimental measurements with digital speckle photography (DSP) is used to study the powder behaviour and for the characterisation of the die filling as part of the process in powder pressing. TheDSP measurements are carried out by recording the powder filling process with a high speed video camera. The image series are then evaluated using an image correlation technique. By this, field data during the filling process can be visualised such as velocity fields and strain fields. These measurements are also supporting the development of a numerical model of the process. In this workthe smoothed particle method (SPH) is used to model the powder filling process. The numerical results are compared with the DSP measurements. The validated model is then used to study the process in more detail, e.g. to evaluate the density distribution after filling. The comparison of DPS measurements and simulations gives similar flow characteristics. Experimental measurements with DSP together with numerical simulation with the SP method are powerful tools to increase the knowledge of powder filling and to improve the process in the future is concluded.

  • 34.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kato, Hidinori
    Nagoya Institute of Technology.
    Nishida, Masahiro
    Nagoya Institute of Technology.
    Modelling and simulation of high velocity loaded iron powder2012Conference paper (Refereed)
    Abstract [en]

    High velocity compaction is a production technique with capacity to significantly improve the mechanical properties of powder metallurgy (PM) parts. The dynamic testing is performed using a modified split Hopkinson pressure bar (SHPB). A specimen is placed between two elastic bars. The impact loading is achieved by a projectile accelerating inside an air gun, which impacts the end of an input bar creating elastic wave propagation. This process is modelled and simulated by using finite element method. The stress and strain history in the specimen during impact are compared with the evaluated experimental values from the strain measured on the input and output bars. The powder material used for the experiments was a press-ready premix containing Distaloy AE, 0.5% graphite and 0.6% Kenolube. In order to model the impact process a constitutive relation describing the powder behaviour taking into account the strain-rate and density variations are proposed. In conclusion, the proposed material model captures the increase in yield stress due to higher strain rates.

  • 35.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kato, Hidinori
    Nagoya Institute of Technology.
    Ogura, Takashi
    Nagoya Institute of Technology.
    Nishida, Masahiro
    Nagoya Institute of Technology.
    Strain Rate Dependent Constitutive Model with Failure for Impact Loading of Metal Powder2013Conference paper (Refereed)
    Abstract [en]

    Few studies have been conducted to investigate the strain rate behavior of metal powders. To achieve better understanding of the strain rate dependency of metal powders, it's necessary to conduct dynamic experiments and numerical simulations e.g. using finite element method. High strain rate experiments of iron powder material have been conducted using the split Hopkinson pressure bar method [1]. The dynamic testing is performed using a modified split Hopkinson pressure bar (Kolsky bar). A specimen is placed between two elastic bars. The impact loading is achieved by a projectile accelerating inside an air gun, which impacts the end of an input bar creating elastic wave propagation. The powder material used for the experiments was a press-ready premix containing Distaloy AE, 0.5% graphite and 0.6% Kenolube. This process is modeled and simulated by using finite element method. In order to model the impact process a constitutive relation describing the powder behavior taking into account the strain-rate and density variations are proposed [2]. The stress and strain history in the specimen during impact is validated against the experimental measurements. To capture the global response caused by cracking during impact, a failure criterion is implemented. In conclusion, the proposed material model captures the increase in yield stress due to higher strain rates and the decrease in stress due to cracking.

  • 36.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Nishida, Masahiro
    Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Japan, Nagoya Institute of Technology.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Ito, Yoshikata
    Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Japan.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Takayama, Tetsuo
    Yamagata University.
    Todo, Mitsugu
    Kyushu University, Kyushu University, 6-1, Kasuga-koen, Kasuga, Fukuoka, Japan.
    Mechanical characterization and modelling of the temperature-dependent impact behaviour of a biocompatible poly(L-lactide)/poly(ε-caprolactone) polymer blend2015In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 51, p. 279-290Article in journal (Refereed)
    Abstract [en]

    Poly(ε-caprolactone) (PCL) is a ductile, bioabsorbable polymer that has been employed as a blend partner for poly(L-lactic acid) (PLLA). An improvement of the material strength and impact resistance of PLLA/PCL polymer blends compared to pure PLLA has been shown previously. To use numerical simulations in the design process of new components composed of the PLLA/PCL blend, a constitutive model for the material has to be established. In this work, a constitutive model for a PLLA/PCL polymer blend is established from the results of compressive tests at high and low strain rates at three different temperatures, including the body temperature. Finite element simulations of the split Hopkinson pressure bar test using the established constitutive model are carried out under the same condition as the experiments. During the experiments, the changes in the diameter and thickness of the specimens are captured by a high-speed video camera. The accuracy of the numerical model is tested by comparing the simulation results, such as the stress, strain, thickness and diameter histories of the specimens, with those measured in the experiments. The numerical model is also validated against an impact test of non-homogenous strains and strain rates. The results of this study provide a validated numerical model for a PLLA/PCL polymer blend at strain rates of up to 1800 s−1 in the temperature range between 22 °C and 50 °C.

  • 37.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Nishida, Masahiro
    Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Japan.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kato, Hidinori
    Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Japan.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Ogura, Takashi
    Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Japan.
    Experimental studies and modelling of high-velocity loaded iron-powder compacts2014In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 268, p. 293-305Article in journal (Refereed)
    Abstract [en]

    A production technique with the capacity to significantly improve the mechanical properties of powder metallurgy (PM) parts is high-velocity compaction (HVC). To extend the usage of the HVC method, detailed knowledge of the HVC process is important. To facilitate the development of production processes, numerical simulations can be utilised. In the development of high-precision simulation models, constitutive data of HVC specimens at high strain rates are required. In this study, the dynamic compressive properties of cylindrical specimens made by HVC were measured using a split Hopkinson pressure bar (Kolsky bar) assembly. For this technique, a specimen is placed between two elastic bars. The impact loading is achieved by a projectile accelerating inside an air gun, which impacts the end of the input bar and generates elastic-wave propagation.The powder material used for the experiments is a press-ready iron-based premix. Among specimens made by HVC and conventional compaction (CC), the effects of the specimen density and the strain rate on the compressive properties, such as failure stress, Young´s modulus and failure behaviour, are investigated. During dynamic compression, the failure behaviour of the specimens was also recorded using a high-speed video camera. The difference in the mechanical behaviour between HVC-pressed specimens and conventionally pressed specimens are also investigated. The stress–strain curves of HVC-pressed specimens are identical to those of conventionally pressed specimens, but the failure behaviour differs are concluded.A well-established numerical method for forming simulations also conducted for powder compaction is the finite element method (FEM). The impact loading of the powder is modelled and simulated using nonlinear three-dimensional FEM. To model the impact process, a constitutive relation for the powder behaviour is proposed, taking into account the strain rate and density variations. To capture the global response caused by cracking during impact, a damage model is implemented. The numerical results in terms of the stress and strain history in the specimen during impact are compared with the experimental measurements. In conclusion, the proposed material model captures the increase in the yield stress due to the higher strain rates and the decrease in stress due to cracking.

  • 38.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    A general computer program for optimised analysis and calculation of bearing arrangements1990In: Ball Bearing Journal, ISSN 0310-6748, no 236Article in journal (Refereed)
  • 39.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Analys av kontakt- och friktionsproblem vid pulver kompaktering: slutrapport1988Report (Other academic)
  • 40.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Bearing life calculation in the bearing application program BEACON1989Report (Other academic)
  • 41.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Computer simulation of powder compaction1987Report (Other academic)
  • 42.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Constitutive modelling of hard metal powder1985Licentiate thesis, monograph (Other academic)
  • 43.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Constitutive models for powder materials1991In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 67, no 2, p. 127-136Article in journal (Refereed)
    Abstract [en]

    Constitutive models to describe the mechanical material behaviour of hardmetal powders are studied. Three classes of constitutive relationships are examined, described as cap plasticity, multisurface plasticity and endochronic plasticity. A representative model of each class is studied in detail, An optimization technique is used to fit the constitutive parameters to empirical test data on multiaxially loaded hardmetal powder specimens. Of all models tested, an endochronic model proposed by Bazant shows the best agreement with the empirical test data. Different phenomena can be simulated with the model by adding certain constitutive functions. It is, however, difficult to fit the model to test data because of the large number of model parameters, most of which have no physical meaning

  • 44.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Explicit versus implicit finite element simulation of metal powder compaction1992In: Numerical methods in industrial forming processes: proceedings of the 4th International Conference on Numerical Methods in Industrial Forming Processes, Valbonne/France, 14-18 September 1992; NUMIFORM '92 / [ed] J.L. Chenot; R.D. Wood; O.C. Zienkiewicz, Rotterdam: Balkema Publishers, A.A. / Taylor & Francis The Netherlands , 1992Conference paper (Refereed)
  • 45.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Modelling and simulation of metal powder pressing1993Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The pressing of hard metal components was analysed with numerical methods. The aim was to calculate the density distribution and the springback during unloading. This thesis concentrated on the following parts; constitutive modelling, explicit versus implicit time integration schemes and contact constraint methods. Three constitutive models for the simulation of the mechanical material behaviour of hard metal powder were evaluated. The models were cap plasticity, multisurface plasticity and endochronic plasticity. The compaction of powder specimen was simulated assuming quasi-static conditions. The method of using explicit time integration of the equations of motion was compared with a traditional method employing implicit time integration. The results show that an explicit code is advantageous in terms of development potential, solution time and ease of use. Alternative constraint methods were evaluated when modelling the contact between powder and tool. A contact constraint method with friction based on direct integration of the equations of the contact interface was proposed. Two specific powder metallurgical parts, a highway engineering tip and a plate for testing crack sensibility, were selected for the analyses. The calculated density distributions were qualitatively in good agreement with experimental results. The springback obtained in the numerical simulation of unloading and ejection processes was in good agreement with measured values.

  • 46.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Numerical simulation of ceramic-metal diffusion bonded and brazed joints1993In: Designing ceramic interfaces II : understanding and tailoring interfaces for coating, composite and joining applications: proceedings of the Second European Colloquium held at Petten on 11 - 13 November 1993 [i.e. 11 - 13 November 1991] / Commission of the European Communities, JRC, Institute for Advanced Materials / [ed] S.D. Peteves, Office for official publications of the European communities , 1993, p. 105-116Conference paper (Refereed)
    Abstract [en]

    finite element method to calculate residual stress fields caused by thermal mismatch in ceramic/metal joints was applied to three problems. These were: an Incoloy 909 cap brazed to a Si3N4 cylinder with Ag-27%Cu filler; diffusion bonding of the same materials with a tungsten interlayer by hot isostatic pressing; and brazing of Al2O3 to Incoloy 909

  • 47.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    On friction models in contact problems1987Report (Other academic)
  • 48.
    Häggblad, Hans-Åke
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Berglund, Daniel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Sundin, Karl-Gustaf
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Formulation of a finite element model for localisation and crack initiation in components of ultra high strength steels2009In: Hot sheet metal forming of high-performance steel, CHS2: 2nd international conference, June 15-17 2009, Luleå, Sweden. Proceedings / [ed] Mats Oldenburg; Kurt Steinhoff; Braham Parkash, Auerbach: Verlag Wissenschaftliche Scripten , 2009, p. 229-237Conference paper (Refereed)
  • 49.
    Häggblad, Hans-åke
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Doremus, P.
    Bouvard, D.
    An International research programme on the mechanics of metal powder forming1996In: Advances in powder metallurgy & particulate materials - 1996: proceedings of the 1996 World Congress on Powder Metallurgy & Particulate Materials ..., June 16 - 21, Washington, DC / sponsored by the Metal Powder Industries Federation / [ed] Terry M. Cadle, Princeton, NJ: Metal powder industries federation , 1996, Vol. Vol. 2, p. 179-192Conference paper (Refereed)
    Abstract [en]

    A collaborative research programme, Mechanics of Metal Powder Forming, has been initiated at PM'94 Conference in Paris. It aims at evaluating the procedures and facilities involved in the numerical modelling of the forming of metal powders by hot and cold compaction, in particular through the identification of bench mark problems. This paper gives a general presentation of this programme and focus on the advancement of cold compaction programme. Material investigated was Distaloy AE (Fe-4Ni-1.5Cu-0.5Mo).

  • 50.
    Häggblad, Hans-åke
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Hockauf, Matthias
    Luleå tekniska universitet.
    Eriksson, Mikael
    Swedish Ceramic Institute.
    Berggren, Carina
    Nobel Biocare AB.
    Simulation of high velocity compaction of powder in a rubber mould with characterization of silicone rubber and titanium powder using a modified split Hopkinson set-up2005In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 154, no 1, p. 33-42Article in journal (Refereed)
    Abstract [en]

    The paper introduces a method for characterization of silicone rubber and titanium powder in high velocity compaction using the split Hopkinson set-up. The impact test data has been used to estimate parameters in constitutive models for rubber and powder. A finite element study has been performed with different geometrical design of the high velocity compaction of titanium powder against an aluminium mandrel using a rubber mould as pressing medium. One goal of this study is to investigate if and how the manufacturing method can be applied for making dental copings. A conclusion of the experimental work is that it is possible to characterize rubber material and powder material for high velocity compaction of metal powder by the use of a modified split Hopkinson pressure bar set-up. The numerical simulation shows qualitatively good agreement with the experience from practical tests. In conclusion, the work shows the possibility to numerically study the geometric design and to optimize the densification behaviour of a complex high velocity compaction process.

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